Metallic materials which are used to form a circuit pattern on an insulator substrate or a semiconductor substrate are required to have the following properties:
(1) Metallic materials used for the above-described purpose must be superior in corrosion resistance; (2) a metal which is used to form a pattern must have excellent adhesion to the surface of an insulator or semiconductor substrate; (3) metallic materials used must have an electrical conductivity which is substantially equal to or higher than that of conventional conducting materials; (4) the difference in thermal expansion coefficient between a substrate and a metal used must be small so that the metal is unlikely to peel off in a repeated cycle in which it is alternately subjected to high and low temperatures; and so forth.
As shown in FIG. 10, a metal 1b such as aluminum, copper, nickel or chromium has heretofore been employed as a metal used to form a circuit pattern on an insulator or semiconductor substrate 6.
However, when such a metal is employed as a wiring material, if portions of a circuit which have different potentials are shorted through water, dissolution of the higher-potential portion is unavoidable.
When in contact with water containing corrosive chemical species such as chlorine ions, sulfate ions, nitrate ions, ferric ions, etc., the electrode is, in many cases, dissolved.
To avoid the above-described problem of corrosion, it is conventional practice to coat the surface of a conductive film circuit with a protective film 7 for prevention of corrosion which is made of a glass, ceramic or plastic material to thereby prevent intrusion of water into the conducting portion of the circuit pattern, as shown in FIG. 10.
The conventional practice suffers, however, from the disadvantage that, even if the thickness of the coating film is increased (e.g., 50 .mu.m or more in the case of a resin material) in order to eliminate water permeability and defects such as pinholes from the coating film formed as described above, water penetration cannot be made zero.
In order to overcome these disadvantages of the prior art, the present inventors proposed an invention of forming a circuit pattern using a corrosion-resistant metal such as tantalum, titanium or niobium.
However, even in this case there has been the problem that oxidation of the surface of a thin film circuit made of a metal such as tantalum causes an increase in the surface resistance and hence a rise in the contact resistance with an external circuit. In addition, when a multilayer thin film circuit is formed, the resistance at a via hole may be increased.
In view of the above-described problems of the prior art, it is an object of the present invention to provide a conductive film circuit having high corrosion resistance and high reliability which is capable of normally performing semipermanently even if it is used in an environment that includes water content without coating the surface of the circuit and the electrode surface with an inorganic or organic protective film for prevention of corrosion and which is not subject to rise in the resistance at a terminal portion or in the resistance at a via hole which would otherwise occur due to oxidation of the surface of the conductive film circuit and the electrode surface and which has no problem of separation even if it is subjected to a temperature cycle over a wide temperature range.